Carboxylic acids may be prepared using a variety of processes. Among the various procedures known, the oxidative cleavage of olefinic hydrocarbons represents a particularly attractive method due to the widespread availability of these types of raw materials. Olefinic hydrocarbons may be oxidized to carboxylic acids using a variety of oxidizing agents, including KMnO.sub.4, K.sub.2 Cr.sub.2 O.sub.7 and RuO.sub.4. These processes are however of little practical interest because of the high cost and toxicity of the oxidizing agents (in particular with regard to RuO.sub.4). There are also serious problems involved with the disposal or recovery of these oxidizing agents and/or the side products generated in the course of such reactions.
The oxidative cleavage of an olefin or a vicinal dihydroxy compound using hydrogen peroxide as the primary oxidant has also been described. The hydrogen peroxide cleavage reaction is reported to be catalyzed by tungstic acid, molybdic acid or related heteropoly inorganic acids. While this procedure represents an improvement over the other oxidative methods discussed above employing costly or toxic reagents, the use of hydrogen peroxide as the primary oxidant still has certain drawbacks. The stoichiometry of the reaction is such that at least 3 or 4 equivalents of hydrogen peroxide are required to accomplish the oxidative cleavage of a diol or olefin respectively (see equations A and B below). More typically, such cleavage reactions are run using a stoichiometric excess of hydrogen peroxide (e.g., 5-6 equivalents of H.sub.2 O.sub.2).
(A) RCHOH--CHOHR'+2 H.sub.2 O.sub.2 .fwdarw.RCO.sub.2 H+R'CO.sub.2 H+2 H.sub.2 O
(B) RCH.dbd.CHR'+3 H.sub.2 O.sub.2 .fwdarw.RCO.sub.2 H+R'CO.sub.2 H+2 H.sub.2 O
While hydrogen peroxide is relatively inexpensive and does not present serious waste disposal problems, hydrogen peroxide is quite reactive and presents safety issues with regard to its handling. Moreover, hydrogen peroxide is sold as an aqueous solution and thus requires the shipping of a considerable amount of water along with the reagent. From both economic and safety standpoints, it would be advantageous if an oxygen containing gas stream, such as air, could be utilized as the major oxidant to effect the oxidative cleavage of olefins and vicinal diols.
The oxidation of vicinal dihydroxy compounds (vicinal glycols) with oxygen in the presence of a catalyst mixture which includes a cobalt (II) compound and a peroxidized tungsten or molybdenum oxide has been reported. This reaction, however, must be run in a polar, aprotic solvent such as dimethylformamide ("DMF"). Since the oxidation of an olefin to a vicinal glycol is typically run in a protic solvent such as t-butanol, this method does not allow direct oxidative cleavage of an olefin to a carboxylic acid without changing the solvent and/or other reaction conditions. In addition, the presence of a polar, aprotic solvent can make the isolation of the desired product more difficult.